Highly Invasive Seaweed Found at Channel Islands National Park

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Date: April 28, 2017
Contact: Yvonne Menard, 805-658-5725

During their annual kelp forest monitoring surveys, National Park Service (NPS) biologists found a highly invasive nonnative kelp Undaria pinnatifida at West Anacapa Island.
Since its initial discovery in June 2016, the invasive seaweed has spread along the entire north coast of the islet, prompting the need for public awareness and support to reduce its spread.
Undaria, the alga that is commonly found in miso soup and is known as wakame, is native to Asia. It first appeared on the west coast of North America in 2000, at Long Beach Harbor. It was first seen in Ventura Harbor in 2007.
Unlike Sargassum horneri, another recently introduced invasive alga, which spreads rapidly due to air bladders that allow it to float in currents, Undaria spreads slowly, unless assisted by transport on boat hulls or by other means.
Now that Undaria has been established, biologists are seriously concerned about its rate of spread increasing. The cold waters at the islands are optimal for its growth. Due to its pattern of quick growth and its large size,Undaria may compete with native seaweeds for space and light and, as a result, may impact the marine ecosystem.
Boaters are the first and best line of defense in limiting Undaria’s rate of spread since eradication efforts are not considered a viable option. They can do so by regularly checking their vessel hulls, fishing gear and nets, moorings, lines, docks, and other structures, especially before leaving the harbor to visit the Channel Islands.
Undaria can easily be removed by grasping it near the holdfast, or root-like structure, pulling it off, and discarding it in the trash. It should not be discarded in the marine environment, as it could release spores that can remain dormant in a microscopic stage for up to two years.
Undaria is easy to identify by its large, golden-brown flattened blades and prominent midrib. Mature individuals have a frilly reproductive structure called a sporophyll at the bottom of the stipe. Undaria reproduces in the winter and spring. To monitor its presence, boaters can keep a special eye out for it attaching to the stern of their vessels or other areas of the hull that are less exposed to high water movement.

Learn more at Marine Invasive Species. 

Last updated: April 28, 2017

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